While the symptoms of the disease for most people are only rash, fever and flu-like effects, catching it during pregnancy can result in the birth of child with microcephaly, a serious birth defect that results in an abnormally small head and brain.

Zika was previously thought to be only transmitted by mosquitoes, but cases have also included blood transfusion and sexual intercourse with an infected person.

In the United States, Dr. Tom Frieden told reporters on Friday, “Our new guidance is that pregnant women should use condoms during sex or abstain if their partner has traveled to an area where Zika has been spreading.”

Frieden also said that he was aware of reports from Brazil that found traces of the virus in saliva and urine samples from infected patients. However, he said that more information is needed on those findings, including the methodology behind them, and the recent guidelines do not address kissing.

"We're still learning more about [the virus in] saliva and how it works in the body," Frieden said. "There's been a total of three cases in the world literature of Zika being present in male secretions."

The World Health Organization has reported 267 Zika outbreaks in countries in the Americas. Brazil has the most Zika infections with more than one million, and Colombia has more than 20,000, the WHO said.